A 3rd Generation Partnership Project (3GPP) based on Wideband Code Division Multiple Access (WCDMA) radio access technology has been developed in the whole world. High Speed Downlink Packet Access (HSDPA), which may be defined as the first evolution of WCDMA, provides radio access technology having high competitiveness in the mid-term future to 3GPP. As a system for providing high competitiveness in the mid-term future, there is an Evolved-Universal Mobile Telecommunications System (E-UMTS).
FIG. 1 shows a network architecture of the E-UMTS. The E-UMTS is an evolved form of a WCDMA UMTS, and the standardization thereof is ongoing in the 3GPP. The E-UMTS is also called a Long Term Evolution (LTE) system. For the detailed contents of the technical specifications of the UMTS and the E-UMTS reference may be made to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”, respectively.
Referring to FIG. 1, the E-UMTS may include a User Equipment (UE), a base station (hereinafter, referred to as an “eNode B” or “eNB”), and an Access Gateway (AG) positioned at the end of the network (Universal Terrestrial Radio Access Network; E-UTRAN) and connected to an external network. Generally, the eNode B may simultaneously transmit multiple data streams, for broadcast services, multicast services and/or unicast services. The AG may be divided into a portion for processing user traffic and a portion for processing control traffic. At this time, an AG for processing new user traffic and an AG for processing control traffic may communicate with each other using a new interface. One or more cells may exist in one eNode B. A plurality of eNode Bs may be connected by an interface for transmitting the user traffic or control traffic. A Core Network (CN) may include the AG and a network node for the user registration of the UE. An interface for distinguishing between the E-UTRAN and the CN may be used. The AG manages the mobility of the UE in the unit of Tracking Areas (TAs). The TA is composed of a plurality of cells. When the UE moves from a specific TA to another TA, the UE informs the AG that the TA of the UE is changed.
Although radio access technology has been developed to LTE based on WCDMA, the demands and the expectations of users and providers have been lastingly increased. In addition, since other radio access technologies have been continuously developed, new technology evolution is required for securing high competitiveness in the future. Decrease in cost per bit, increase in service availability, flexible use of a frequency band, simple structure, open interface, suitable UE power consumption and the like are required. The standardization of the subsequent technology of the LTE is ongoing in the 3GPP. In the present specification, the above-described technology is called “LTE-Advanced” or “LTE-A”.
In the case of LTE, in downlink transmission, Multiple-Input Multiple-Output (MIMO) is applied and spatial multiplexing is used. However, in uplink transmission, due to problems associated with efficiency of a power amplifier of a UE and the arrangement of antennas, spatial multiplexing is not considered. However, in order to maximize the use of frequency resources or a demand for high-speed communication, the LTE-A requires spatial multiplexing using the MIMO in uplink transmission. In detail, the LTE-A requires spatial multiplexing up to a maximum of four layers in uplink transmission. In addition, the LTE-A requires transmission of a maximum of two transmission blocks via one subframe per component carrier in the case of multiplexing by a single user in uplink transmission. The component carrier refers to a basic frequency block used in carrier aggregation. Carrier aggregation refers to technology for logically combining a plurality of frequency blocks to support a wideband, and the LTE-A uses the frequency aggregation technology, for wideband.